Friday, October 1, 2010

The Cosmic Quintessence

The Cosmic Quintessence
From earliest times, humans have wondered about the Universe – how did it come into being and what is it made of? It seems that answers remain beyond our grasp.
David Hambling
September 2010
FT267

Something is wrong with the Universe, or at least our understanding of it. Previously, in the words of Arthur Dent, “Most of it seemed to make sense at the time.” But new discoveries have upset our tidy view of the Cosmos, filling it with inexplic­able Dark Matter and Dark Energy. As the magazine of unexplained phenomena, FT should cover most of the Universe. Or might scientists be able to make sense of it all again?

Things started well at the beginning of the 20th century. Astronomers discovered that in every direction there were galaxies moving away from us. They also found that the further away a galaxy was, the faster it was going. Their measurements showed that this expansion was consistent with all observed matter having exploded outward from a single point in the distant past. The rate of expansion was slowing down due to the effect of gravity, and the only question was whether there was enough mass to cause the Universe to eventually collapse in on itself again.

While consistent enough, the new notion went down badly with those who preferred an eternal ‘steady state’ theory of the Universe. Fred Hoyle dismissively referred to the new theory as “this ‘big bang’ idea” in a BBC radio broadcast in 1949. The name stuck, and the Big Bang has been with us ever since.

However, close observations of galaxies revealed that something was missing. The amount of material that astronomers could see in stars and nebulæ was not enough to account for the gravit­ational force holding galaxies together. The missing material, known as Dark Matter, weighs about five times as much as visible matter. [1] There have been various theories about where this invisible material might be hiding.

Early suggestions of galaxies shielded by dust clouds, or antimatter galaxies, were ruled out as these would have been detected by the radiation they emitted. Giant black holes were also excluded, as they can be spotted by ‘gravitational lensing’ effects. One possibility is that the Dark Matter might take the form of invisible brown dwarf stars – like the one that Andy Lloyd thinks is lurking at edge of the Solar System [FT265:38]. Such objects are known as Massive Compact Halo Objects or MACHOs. This is to contrast them with the other likely contender, elusive subatomic part­icles which have mass but do not interact with ordinary matter, known as Weakly Interact­ive Mass­ive Particles or WIMPs. (That’s physicist humour for you).

Neutrinos are ghostly sub­atomic particles; they are emitted by the Sun, and thousands are streaming through you at this moment without ever being noticed. Originally they were thought to be massless, but in 2002 they were shown to have mass. Was this the missing Dark Matter? Unfortunately not; each neutrino weighs about a millionth as much as an electron, not nearly enough to account for the missing matter.

The giant orbiting Hubble telescope should have helped clear things up. Instead, it made things much worse. In 1998, precise measurements from very distant galaxies showed that the rate of expansion of the Universe was not decreasing due to gravitational pull, as expected. It was accelerating. Some sort of immense force is pushing everything outwards. Known as Dark Energy, this turns out to be even greater than Dark Matter. The latest figures for the Universe are: Dark Energy – 70 per cent; Dark Matter – 25 per cent; Actual Things We Can See And Know About – 5 per cent.

Dark Energy might simply be a property of space. Or it might be some sort of dynamic energy field that fills space and creates a force; this possible field has been called Quintessence after the fabulous Fifth Element postulated by alchemists.

“If Quintessence is the answer, we still don’t know what it is like, what it interacts with, or why it exists,” concludes a description on NASA’s website, [2] succinctly describing our current state of ignorance. NASA’s response is to build an even bigger and better telescope in a Joint Dark Energy Mission to get an accurate picture of the historic expansion of the Universe and how it has changed. If they can get funding.
There are other problems much closer at hand. Probes sent to the edges of the Solar System are not where they ought to be. In particular, two Pioneer probes, 10 and 11, which were sent far beyond Jupiter, have instruments that allow their location and speed to be measured with very high precision. Both are subject to an unexplained slowing-down force.

Another anomaly crops up right next to the Earth. For years, scientists have been using the “slingshot effect” to give spacecraft a boost by having them pass close to a planet. In some cases, probes have a complicated traject­ory that uses the Earth for this effect. Except that the change in speed has not been as expected: sometimes they end up measurably faster than ought to be poss­ible. The Rosetta spacecraft has passed by the Earth three times, but has experienced the anomaly only once. [3]

Perhaps some new Einstein will succeed in drafting a new set of laws of physics that will neatly account for these anomalies. Certainly, plenty of scientists are trying. If they succeed, then we may be able to discard weird notions like Dark Energy and Dark Matter, and our spacecraft will behave themselves. Until then, those who think we understand the Universe are approximately 95 per cent wrong.